1. Field of the Invention
The present invention relates to a dual mask process for making a second pole piece layer of a write head with a high resolution narrow track width second pole tip and more particularly to first and second photoresists masks that are photopatterned separately so that the first photoresist mask masking the second pole tip is thin for promoting high resolution of the second pole tip with a narrow track.
2. Description of the Related Art
The heart of a computer is an assembly that is referred to as a magnetic disk drive. The magnetic disk drive includes a rotating magnetic disk, write and read heads that are suspended by a suspension arm above the rotating disk and an actuator that swings the suspension arm to place the read and write heads over selected circular tracks on the rotating disk. The read and write heads are directly mounted on a slider that has an air bearing surface (ABS). The suspension arm biases the slider into contact with the surface of the disk when the disk is not rotating but, when the disk rotates, air is swirled by the rotating disk adjacent the ABS of the slider causing the slider to ride on an air bearing a slight distance from the surface of the rotating disk. When the slider rides on the air bearing the write and read heads are employed for writing magnetic impressions to and reading magnetic impressions from the rotating disk. The read and write heads are connected to processing circuitry that operates according to a computer program to implement the writing and reading functions.
The write head includes a coil layer embedded in first, second and third insulation layers (insulation stack), the insulation stack being sandwiched between first and second pole piece layers. A gap is formed between the first and second pole piece layers by a nonmagnetic gap layer at an air bearing surface (ABS) of the write head. The pole piece layers are connected at a back gap. Current conducted to the coil layer induces a magnetic field into the pole pieces that fringes across the gap between the pole pieces at the ABS. The fringe field writes field signals in the form of magnetic bits of information in tracks on moving media, such as in circular tracks on a rotating disk.
The read head senses the field signals as the disk rotates. This is typically accomplished by a sensor that changes resistance proportional to the magnetic field imposed on the sensor by the magnetic bits of information. A sense current is conducted through the sensor and the resistance changes in the sense current circuit are processed by processing circuitry as playback signals. First and second leads are connected to the sensor for conducting the sense current therethrough. The sensor and the first and second leads are located between first and second read gap layers and the first and second gap layers are located between first and second shield layers.
Multiple magnetic head assemblies are constructed in rows and columns on a wafer by various thin film deposition-techniques. After constructing the magnetic head assemblies on the wafer, the wafer is diced into rows of magnetic head assemblies and lapped in order to form each magnetic head assembly with an air bearing surface. The row of magnetic head assemblies is then diced into individual magnetic head assemblies and one or more magnetic head assemblies is mounted in a magnetic disk drive. The metallic components of the read and write head of each magnetic head assembly, except for the metallic components of the read sensor, are typically constructed by what is known in the art as frame plating. Frame plating comprises sputter depositing a seed layer on the wafer, spinning a layer of photoresist on the seed layer, light exposing the photoresist layer in areas which are to be removed, assuming the photoresist is a positive photoresist, developing the photoresist to remove the light exposed portions of the photoresist layer leaving an opening where the metallic component is to be formed, electroplating the metallic component into the opening using the seed layer as an electrical return path, and then removing the photoresist layer. This process is also referred to in the art as photolithography patterning or photo patterning.
The first and second shield layers of the read head are typically formed by frame plating or by sputter deposition. After construction of the second shield layer the second shield layer is employed as a first pole piece layer for the write head or a dielectric isolation layer is formed on top of the second shield layer followed by construction of the first pole piece layer by frame plating on the isolation layer. When the second shield layer is employed as the first pole piece layer the magnetic head assembly is referred to as a merged magnetic head whereas when the isolation layer is employed the magnetic head assembly is referred to as a piggyback head. The second shield/first pole piece layer or first pole piece layer has a yoke region which is located between a pole tip region and a back gap region. The pole tip region is defined between the air bearing surface and the location where the second pole piece layer first commences to widen after the air bearing surface. After constructing the first pole piece layer the write gap layer is sputter deposited on the pole tip portion of the first pole piece layer.
Either before or after construction of the write gap layer an insulation stack with one or more coils embedded therein is constructed on the yoke region of the first pole piece layer. Each insulation layer of the insulation stack is typically constructed by spinning a layer of photoresist on the wafer, exposing the photoresist layer to light in regions that are to be removed, developing the photoresist layer to remove the light exposed portions and then baking the photoresist layer at a high temperature until it hardens. The edges of the baked photoresist layer are typically rounded or curved by this process and the curved edge facing the air bearing surface is quantified by an aspect angle .theta. where .theta. is the angle that the forward edge of the baked photoresist layer makes with a horizontal. After constructing the first insulation layer, the write coil layer is frame plated thereon followed by construction of a second photoresist layer on the write coil layer. In some write heads, a second write coil layer is then frame plated on the second insulation layer followed by construction of a third and, optionally, a fourth photoresist insulation layer on the second write coil layer. It can be visualized that the construction of the insulation stack, whether it includes one or two coils, results in a high profile insulation stack close to the air bearing surface where a second pole tip of the second pole piece layer is to be constructed.
The second pole piece layer is also constructed by frame plating. A photoresist layer is spun on the wafer on top of the insulation stack as well as on top of the write gap layer between the insulation stack and the air bearing surface. During the spinning process the photoresist layer planarizes across the wafer causing the photoresist to be very thick in the pole tip region between the curved forward edge of the insulation stack and the air bearing surface and somewhat thinner on top of the insulation stack. It is necessary that the photoresist have a sufficient thickness on top of the insulation stack in order to frame plate the yoke portion of the second pole piece layer. Assuming a thickness of 3.5 .mu.m for the yoke portion of the second pole piece layer, the thickness of the photoresist on top of the insulation stack should be approximately 4.0 .mu.m. This can result in the thickness of the photoresist layer between the insulation stack and the ABS of 8 .mu.m to 12 .mu.m. Unfortunately, this thickness does not permit constructing a second pole tip with high resolution and a narrow track.
Efforts continue to construct high resolution second pole tips with a submicron track. By decreasing the track width of the second pole tip the magnetic storage capability or capacity of the magnetic disk drive is increased. These kinds of efforts have increased the storage capacity of computers from kilobytes to megabytes to gigabytes. Since the second pole tip may also be only 3.5 .mu.m in height the light exposure step in the frame plating of the second pole piece layer must penetrate 5 to 8 .mu.m in the photoresist layer in the pole tip region before the light exposure step light exposes the second pole tip site where the second pole tip is to be frame plated. As the light penetrates the photoresist layer in the pole tip region it disperses laterally in the same manner as light disperses in a column of water. This provides poor definition for the side walls of the second pole tip which defines the track width. Accordingly, the thick photoresist layer portion in the pole tip region can result in irregularly shaped side walls which are not precisely formed. Another problem that can occur is reflective notching by the light during the light exposure step. The seed layer sputter deposited on the wafer becomes a light reflector on the insulation stack. When the light is directed downwardly for light exposing the site where the second pole tip is to be formed, light is reflected from the sloping surfaces of the forward portion of the insulation stack into regions laterally adjacent the first and second side wall sites of the second pole tip causing a notching of the photoresist layer beyond the first and second side walls after the photoresist layer is developed. This causes the second pole tip to be frame plated with irregularly shaped first and second side walls which extend beyond the desired track width of the second pole tip. Accordingly, there is a strong felt need to provide an improved photo process for constructing a narrow second pole tip with high resolution.